During the weaving of textiles, the threads are exposed to considerable mechanical strain. Prior to weaving on mechanical looms, warp yarns are often coated with size starch or starch derivatives in order to increase their tensile strength and to prevent breaking. The most common sizing agent is starch in native or modified form, yet other polymeric compounds such as polyvinylalcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) or derivatives of cellulose (e.g. carboxymethylcellulose (CMC), hydroxyethylcellulose, hydroxypropylcellulose or methylcellulose), may also be abundant in the size.
In general, after the textiles have been woven, the fabric proceeds to a desizing stage, followed by one or more additional fabric processing steps. Desizing is the act of removing size from textiles. After weaving, the size coating must be removed before further processing the fabric in order to ensure a homogeneous and wash-proof result. The preferred method of desizing is enzymatic hydrolysis of the size by the action of amylolytic enzymes.
Increasing amounts of cotton wax and other lubricants are applied to yarns in order to increase the speed of cotton weaving. Also waxes of higher melting points are being introduced. Wax lubricants are hydrophobic substances obtained by esterification of long chain alcohols and fatty acids, and they are predominantly triglyceride ester based lubricants. After desizing, the wax either remains or redeposits on the fabric and as a result, the fabric gets darker in shade, gets glossy spots, and becomes more stiff.
International Patent Application No. WO 93/13256 (Novo Nordisk A/S) describes a process for the removal of hydrophobic esters from fabric, in which process the fabric is impregnated during the desizing step with an aqueous solution of lipase. This process has been developed for use in the fabric mills only, and is carried out using existing fabric mill equipment, i.e. a pad roll, a jigger, or a J box.
For the manufacture of clothes, the fabric is cut and sewn into clothes or garments, that is afterwards finished. In particular, for the manufacture of denim jeans, different enzymatic finishing methods have been developed. The finishing of denim garment normally is initiated with an enzymatic desizing step, during which garments are subjected to the action of amylolytic enzymes in order to provide softness to the fabric and make the cotton more accessible to the subsequent enzymatic finishing steps.
For many years denim jeans manufacturers have washed their garments in a finishing laundry with pumice stones to achieve a soft-hand as well as a desired fashionable "stone-washed" look. This abrasion effect is obtained by locally removing the surface bound dyestuff. Recently cellulytic enzymes have been introduced into the finishing process, turning the stone-washing process into a "bio-stoning process".
The goal of a bio-stoning process is to obtain a distinct, but homogeneous abrasion of the garments (stone-washing appearance). However, the dark shades arising from wax on the fabric greatly reduce the stone-washing quality, and the stiffness of the fabric causes more rigid folds. As a result, uneven stone-washing ("streaks" and "creases") occur. In consequence repair work ("after-painting") is needed on a major part (up to about 80%) of the stone-washed jeans that have been processed in the finishing laundries.
The problem of streaks and creases on the finished garments can generally be traced back to the desizing step. Initially the fabric is stiff and very often creases have been formed on the garments during packing and transport. Streaks are rapidly formed at exposed places--such as creases--if the garment is abraded when still stiff. Therefore it is very important that denim garments are quickly softened in an efficient desizing and/or finishing process.